One of the most promising approaches in immunotherapy is activating antitumor immunity in patients by 'checkpoint blockade' referring to the use of antibodies that block immuno-inhibitory pathways switched on by cancer cells. A growing number of cancers that respond to these checkpoint blockades have now been described in patients. Antibodies that block CTLA-4 (ipilimumab) and PD-1 (pembrolizumab) have been approved to treat patients with melanoma, renal-cell carcinoma and non-small-cell lung carcinoma with durable clinical responses. However as checkpoint blockade becomes a promising therapeutic avenue for cancer therapy, current preclinical models are not able to recapitulate the antitumor immune responses mediated by checkpoint blockade therapies. This is partly because of the inherent differences between the mouse and the human immune systems. HuMurine Technologies was founded in 2008 as a CRO to standardize and optimize the construction of 'humanized' mice (Hu-M(tm) platform) stably engrafted with a human immune system. The Hu-M(tm) platform has been successfully implemented for evaluating therapies that specifically target the human immune system in a wide range of diseases models. In order to address the high unmet need for a robust preclinical platform for testing the efficacy and safety of novel immunotherapies HuMurine has partnered with Champions' Oncology to develop and validate the PDX/ Hu-M(tm) platform using the approved immune- checkpoint modulators Ipilimumab and Pembrolizumab. This development process will also included consultation with potential end users of the platform including major pharmaceutical companies and biotech's which demonstrates a strong commercialization plan for the platform post-validation. This proposal aims to address a part of NCI's provocative questions initiative about the development of appropriate model systems to understand the human immune responses within the tumor microenvironment. Validated of this novel PDX/Hu-M(tm) platform would significantly reduce the high attrition rates of immunotherapeutics in clinical trials. The Specific Aims of this proposal are: Aim 1: Determine if Ipilimumab treated HLA-A2- matched melanoma PDX/ Hu-M(tm) mice generates a tumor- specific T cell response. Aim 2: Determine antitumor efficacy of combinational checkpoint blockade of CTLA-4 and PD-1 in HLA-A2 matched melanoma and NSCLC PDX/ Hu-M(tm) mice.